Microlithography is used for producing microstructured components, for example integrated circuits. The microlithography process is carried out with a lithography apparatus including an illumination system and a projection system. The image of a mask (reticle) illuminated via the illumination system is in this case projected via the projection system onto a substrate (for example a silicon wafer) which is coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection system, in order to transfer the mask structure to the light-sensitive coating of the substrate.
The projection system can have a multiplicity of refracting and/or reflecting optical elements, for example lenses or mirrors. Each optical element can be received or held in a holding device, in particular in a mount. A force-fit or frictional and/or form-fit connection can in this case be provided between the optical element and the holding device. In the operation of the lithography apparatus, the optical elements can be moved and accelerated. A relative movement between the optical element and the holding device assigned to the latter is undesirable.
In order to secure the position of the optical element with respect to the holding device, a defined clamping force is used with which the optical element is clamped between two components of the holding device. During the acceleration of the optical element, a frictional force resulting from the clamping force acts counter to acceleration forces acting on the optical element. In order to prevent a movement of the optical element with respect to the holding device, it is therefore desirable that the frictional force is always greater or at least equal to the acceleration forces. The clamping force therefore always has to be maintained at a sufficient level.
To adjust the optical element, it is also desirable that a contact face between the optical element and the holding device is as small as possible, preferably involving a punctiform or linear contact. However, a punctiform or linear contact is unfavourable in terms of the extent of the so-called surface pressure between two connection partners. If the admissible surface pressure is exceeded, this can lead to undesired stress-induced changes of the optical properties of the optical element.